This invention relates to lubricating oil compositions having significantly low levels of sulfur, phosphorous and ash and which are especially suitable for use in conjunction with fuels having ultra-low sulfur content.
Internal combustion engines, such as automobile spark ignition engines, require the use of a lubricant to protect engine parts from wear, to promote friction reduction, to suppress deposits formation and to improve engine cleanliness. Mineral or synthetic lubricating oils by themselves will not provide these properties at levels now required by users. Therefore, contemporary engine oil technology uses various additives in conjunction with base lubricating oils to enhance the properties of the base oil in at least one and typically in a number of different aspects.
Among the engine oil additives contained in most commercially available internal combustion engine oils are zinc dithiophosphates and metallic detergents. The former are included for their antiwear properties and oxidation inhibiting characteristics. The latter are included for their detergent properties. These additives are rich in sulfur, phosphorous and ash content and their presence presents problems in meeting ever more severe engine performance requirements. For example, sulfur compounds in engine exhaust gases are known to poison catalysts used in exhaust systems to reduce NOx emissions; and phosphorous is known to poison the hydrocarbon conversion catalysts used in those systems. In addition there is a need to lower ash levels to reduce plugging of particulate trap after-treatment devises.
Simply lowering the amount of zinc dithiophosphate and metallic detergents is not a practical solution to the problem because of the concomitant lowering of the antiwear properties and oxidation inhibition properties as well as the decreased detergency of the oil.
An object of the present invention is to provide a low sulfur, detergents is not a practical solution to the problem because of the concomitant lowering of the antiwear properties and oxidation inhibition properties as well as the decreased detergency of the oil.
Another object is to provide an engine oil for use in conjunction with low sulfur fuels ( less than 350 ppm) for enhanced automotive emission control.
The present invention provides a low sulfur, low phosphorous, low ash lubricating oil composition for internal combustion engines which is especially useful in conjunction with fuels having a sulfur content of less than 350 ppm by weight. The lubricating oil composition of the present invention comprises:
(a) a major amount of a base oil of lubricating viscosity and having a sulfur content below about 300 ppm based on the weight of base oil;
(b) about 0.5 wt % to about 10 wt % of a boron-containing ashless dispersant;
(c) about 0.05 wt % to about 1.50 wt % of a molybdenum containing friction reducing additive;
(d) about 0.05 wt % to about 5.0 wt % of at least one kind of metal-type detergent selected from the group consisting of sulfonates, phenates and salicylates; and
(e) 0.10 wt % to 0.75 wt % of a zinc dithiophosphate.
The lubricating compositions of the present invention have a total base number less than 4, and preferably between about 3.25 to about 3.75, a phosphorous content less than 0.048 wt %, sulfated ash of less than 0.5 wt % and total sulfur content less than 0.18 wt %.
The lubricating composition of the present invention is particularly suitable for reducing friction and wear in engines combusting an ultra low sulfur fuel compared with lubricants containing greater amounts of sulfur, phosphorus and ash. Thus another embodiment of the invention is a method of reducing friction and wear in such engines by lubricating them with the composition broadly defined above.
The base oil used in the composition of the present invention will contain less than 300 ppm sulfur and may be a mineral or synthetic oil or blends thereof. Suitable base oils include Group II, III, IV and V basestocks as defined by the API. Preferably the base oil is a Group IV or V basestock. Typically, the base oil will have a viscosity range of from about 15 to about 8000 cSt at 40xc2x0 C. An especially preferred base oil is a blend of synthetic base oils such as polyalpha olefins (PAO""s), poly internal olefins (PIO""s), polyesters, alkylated aromatics, polybutenes, hydroprocessed oils and gas to liquid oils (GTL""s) such as liquid base stock derived from hydroisomerized Fischer-Tropsch waxes having a viscosity in the range of 3 to 26.1 cSt at 100xc2x0 C.
In the lubricating oil composition of the present invention a boron-containing ashless dispersant and/or metallic detergent is employed. Examples of suitable boron-containing ashless dispersants are compounds prepared by boration of succinimide, succinic ester, benzyl amine and fatty acid amides. The particularly preferred boron-containing ashless dispersant is a succinimide or succinic ester/amide derivative containing 0.1 to 5.0 wt % boron such as boronated mono and bis PIBSA/PAM. Typically the Mn of the PIB moiety in the preferred dispersant will be in the range of about 300 to about 4000. The boron-containing ashless dispersant is incorporated in the composition in an amount of about 0.5 to about 10 wt % based on the total weight of the composition. Boron free ashless dispersants optionally may be combined with the boron-containing dispersants.
Descriptions of dispersants can be found in the following U.S. Pat. Nos. 5,356,552; 4,904,401; 4,941,984; 4,904,401; 5,169,564; 5,133,900; 6,010,986; 6,159,912; and the following EP documents: 0 721 978 A2; 0 699 738B1; 0 389 573B1.
Regarding the molybdenum-containing additive used, mentioned is made of molybdenum diorganic dithiocarbamates molybdenum diorgano dithio phosphate, and moly carboxylates. Particularly preferred are trinuclear molybdenum compounds having the formula Mo3S7(dtc)4, Mo3S4(dtc)4 and mixtures thereof where dtc represents diorganodithiocarbamate ligands. Such compounds are disclosed in U.S. Pat. No. 6,010,987 (see also U.S. Pat. Nos. 5,696,065; 5,627,146; 5,631,213; 3,509,051. The amount of molybdenum containing additive will be in the range of about 0.05 to about 1.50 wt % based on the total weight of the composition.
Examples of metal-type detergents are the alkaline metal salts of sulfonates, phenates and salicylates. Generally the alkali metal used are calcium, magnesium and barium. These detergents may be employed singly or in combination. The amount of metal-type detergent used is in the range of about 0.1 to about 5.0 wt % based on the total weight of the composition. Optionally these metal detergents may be combined with boron containing metal detergents. Examples of suitable boron-containing metallic detergents are compounds prepared by boration of calcium, magnesium or other metallic phenates, sulfonates, phenates, salicylates, carboxylates containing 0.1 to 5.0 wt % boron. The boron containing metallic detergent may be incorporated in the composition in an amount of about 0.1 to about 5 wt % based on the total weight of the composition.
As the zinc dialkyldihiophosphate (ZnDTP) to be used in the lubricant composition of the invention, such compound may be represented by the formula (1): 
where R1 and R2 are independently the same or different primary, secondary alkyl groups of 3 to 20 carbon atoms. Information with respect to ZDTP may be found, for example, in U.S. Pat. No. 4,904,401. The ZDTP will constitute 0.1 to 0.75 wt % of the composition.
The composition of the invention may and preferably will include antioxidants such as phenolic and aminic type antioxidants well known in the art. Mixtures of these are especially suitable. Effective amounts of such additives are typically in the range of about 0.5 wt % to about 5.0 wt % based on the total weight of the composition.
The compositions of the invention may also include a VI improver, defoamant and seal swelling agent. Typical VI improvers include polymethacrylates, olefin polymers, copolymers and terpolymers (butene, ethylene-propylene, ethylene-butene, etc.), styrene-diene copolymers and the like. Typical defoamants include silicones and poly-acrylates/methacrylates. Typical seal swelling agents include mono-esters, dibasic acid esters and polyol esters.
Among the features of the compositions of the invention is that they have low sulfur, phosphorous and ash. For instance the total sulfur content is less than 0.18 wt %, the phosphorous less than 0.048 wt % and the sulfated ash less than 0.5 wt %.
The compositions of the invention are particularly useful in conjunction with fuels having ultra-low sulfur content, i.e., a sulfur content below about 350 ppm.
The invention is further illustrated with reference to the following Examples.